I often go on about how software applications often diverge from, or uniquely implement, documented standards for formatting files that they create. Some software vendors are aware of, and document these deviations. Adobe are a good example of this with their software and in particular their implementation of extensions in writing files that adhere to the PDF version 1.7 formatting standard. Below is an extract from the wikipedia entry on PDF with my emphasis in italics at the bottom:   “Adobe’s PDF specifications    Adobe changed the PDF specification several times and continues to develop new specifications with new versions of Adobe Acrobat. There have been nine versions of PDF with corresponding Acrobat releases:[10]      (1993) – PDF 1.0 / Acrobat 1.0    (1994) – PDF 1.1 / Acrobat 2.0    (1996) – PDF 1.2 / Acrobat 3.0    (1999) – PDF 1.3 / Acrobat 4.0    (2001) – PDF 1.4 / Acrobat 5.0    (2003) – PDF 1.5 / Acrobat 6.0    (2005) – PDF 1.6 / Acrobat 7.0    (2006) – PDF 1.7 / Acrobat 8.0    (2008) – PDF 1.7, Adobe Extension Level 3 / Acrobat 9.0    (2009) – PDF 1.7, Adobe Extension Level 5 / Acrobat 9.1     The ISO standard ISO 32000-1:2008 is equivalent to Adobe’s PDF 1.7. Adobe declared that it is not producing a PDF 1.8 Reference. The future versions of the PDF Specification will be produced by ISO technical committees. However, Adobe published documents specifying what extended features for PDF, beyond ISO 32000-1 (PDF 1.7), are supported in its newly released products. This makes use of the extensibility features of PDF as documented in ISO 32000-1 in Annex E. Adobe declared all extended features in Adobe Extension Level 3 and 5 have been accepted for a new proposal of ISO 32000-2 (a.k.a. PDF 2.0).[11]    The specifications for PDF are backward inclusive. The PDF 1.7 specification includes all of the functionality previously documented in the Adobe PDF Specifications for versions 1.0 through 1.6. Where Adobe removed certain features of PDF from their standard, they too are not contained in ISO 32000-1.[1]    PDF documents conforming to ISO 32000-1 carry the PDF version number 1.7. Documents containing Adobe extended features still carry the PDF base version number 1.7 but also contain an indication of which extension was followed during document creation.”   I added the emphasis to make a point. For understanding how files are internally structured it is not always enough to just know the formatting standard adhered to when files were created (e.g. PDF version 1.7). Sometimes we need more information about how the particular application chose to interpret or, as in the example above, implement the standard. This information could be represented in many cases simply by knowing what the creating application was. This is shown/implicitly acknowledged in the Wikipedia extract by the inclusion of the application association with the name of each PDF version listed in the list of versions.